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WAVE TRANSFEHRING CIRCUITS FOR COMMUNICATION SYSTEMS a" ii Maw/770k:

' John M/Y/S lip/V Sept. 9 1924.

"with this invention.

Patented. Sept. '9,

UNITED STATES PATENT OFFICE.

JOHN MILLS, 01F .NYO'MING, NEW JERSEY, ASSEGNOR T WESTERN ELECTRIC. COM- PANY, INGDRPUBATED, OE NEV YC-RK, N. A CORIGEKATION OF NEW YORK.

"WAVE-TRANSFEBRING CIRCUITS FOR COMMUNICATION: SYSTEMS Application filed June 1,

To all LO/L077), it may concern:

Be it known that l, JOHN Mitts, a citizen oi? the United States, residing at Wyoming, in the county of Essex and State of New J ersey. ha ve invented certain new and useful improvements in Wave-Transterring Circuits ior Comn'iunication Systems, oi'f which the following a lull clear concise and exact description;

This invention relates to radio transmis sion mid one object is to secure simultaneous sending and receiving Without the use of several a utennzi. This object is accomplished by employing novel means for alternately ronnc ring the transmitting and receiving apparatus to the antenna in rapid succession.

Other objects will appear from a perusal of the following detailed description, after which the i'tures believed to he allowable are set to r n1 the claims.

This invention will be more clearly understood by reference to the drawing which represents a combined transmitting and re ceiving system constructed in awordance Referring to the vlig- *nts a generator oi? high lreosci rations which may be of any suitable :li'orun but is here shown u i an oscillating vzuiuum tube. The oscillation generao ator comprises a closed tuned circuit having an inductance and a capacity serially included therein with the anode and grid of a thermionic repeater connected respectively to the terminals of the capacity and the tilaniei'itury cathode connected to an intermediate point in the inductance. A space current battery is included in the anodccathode circuit. 2 represents a microphone circuit in which are produced alternating currents of telephonic frequency. By means of a transformer this circuit 2 is connected to the input terminals of a thermionic amplilie]? Whose function is to increase the cited tire amplitude of the telephone currents produced in circuit 2. The telepl'ione currents in circuit 2 cause a corresponding voltage to be impressed across the grid and cathode of the amplifying tube, thereby causing corresponding but greater changes of currentand voltage in the. output circuit connected to the anode and the cathode thereof. The means shown typifies any suitable amplifyirg means which might be utilized. The output ircuit of amplifier is connected to the input circuit of a thermionic modu- 1916. Seria1'No.101,18l.

lating device el by which connection. the impedance of the tube 4- is made to vary in accordance with the signals originating in the circuit 2. The output circuit of the high frequency generator 1 is also connected to the input circuit of the modulator 4 with the result that in the output circuit of the latter there appear high frequency oscillations, modulated in amplitude in accordance with the signal waves due to the microphone. These modulated waves in the output circuit at are next in'iprcssed upon the input circuit of an amplifier or a system of amplifiers 5 Whose common output circuit contains a coil. (5 which is coupled to a coil in the antenna T.

The method of periodically connecting this transmitting system to the antenna consists in rendering the generator 1 alternately eflicient and ii'iei'licient by means of the up paratus next to be described. It is welllmown that it the potential of the grid of a thern'iionic amplifier is made to take a suliiciently high negative value with respect to the potential oi the cathode the space current in the amplifier may be reduced to zero. and consequently its efficiency is also reduced to zero. When the space current of the tube of the generator 1 is thus diminished, it Will be clear that no signals will be transmitted from the antenna 7. The method of securing this periodic reduction in space currents will now be explained. 8 represents a generator of oscillations of frequency above the lii'nitoi' audibility, but considerably below the frequency generated by the generator 1. It is proposed to impress these oscillations upon the input circuit of the generator 1 and thereby cause the resultant voltage over that circuit to vary periodically by an amount su'l'licient to reduce the space current to zero during halt the time of operation. The generator 8 would normally Furnish from its output circuit an approximately sinusoidal currentwhereas it is desirable that the electromotive force impressed upon the input circuit of generator 1 shall be an approximately fiat topped wave. A flat topped wave is one which has a substantially constant potential for each hall wave. l Vhen the flat topped wave is negative, the vacuum tube is rendered inoperative and here it is not altogether essential that the wave be flat topped, that is, that the potcntial be constant provided that the potential is sutliciently negative to keep the tube inoperative. WVhen the flat topped wave is positive, however, the tube is operative but here it is essential that the wave be flat topped, that is, that the voltage be constant so that only the variable signal currents will apply a variable potential to the tube whereby the space current in the tube will be con trolled only by the variable signal current. When the halves of the wave act alternately to render inoperative each of a pair of vacuum tube devices, it is therefore preferable that both halves of the wave be flat topped.

As explained, page 62 et seq.l5yerlys Fouriers Series, a flat topped wave may be represented by the equation :A (sin m+ sin 3m+ sin 550, etc.) where A is a numeric and :0 represents an where N is an integer.

This form of wave is secured by connecting the output circuit of generator 8 to the input circuit of a power limiting device 9. The device 9 may consist of a thermionic repeater having a high resistance 19 in the output circuit. Such a resistance limits the output current to a definite maximum value even though high potentials are applied to the input circuit. Any other suitable arrangement, however, may be utilized as a power limiting device for effecting the flat tening of the wave. Such a device has the effect of cutting off the top of the wave at a predetermined value. The device 9 limits the power and produces a flat topped wave,

since, for current above a given value, the

fall of potential across the resistance 19 becomes effective to prevent further substantial increase of the current. The frequency generated by the device 8 will be above the limit of audibility as hereinbefore stated and preferably of the order of 10,000 to 30,000 cycles per second. Transformer 20 serves to impress the flat topped wave upon the input resistances 22 of the amplifying devices 10 and 18. A condenser 21 connected across the secondary of transformer 18 may have any suitable value of capacity. but preferably a small value. A flat topped wave then appears in the output circuit of the power limiting device 9, and is impressed upon the input circuit of the generator 1 through the amplifier 10 and switch 11.. whose functions are to provide for the tuning of the system without the added complication of the control generator 8 and its associated circuits. The function of amplifier 10 is to adjust the controlling voltage at the terminals of generator 1 to the correct value.

In receiving signals, a tuned circuit 12 is coupled to the antenna and supplies power to the input circuit of a power limiting de vice 13, whose function is to prevent excessive disturbances in the receiving system when messages are being transmitted from the local station. The power limiting device 13 may be similar to the device 9 as shown, or may be any suitable device for limiting the transferred energy. The output circuit is coupled through another tuned circuit 1s to the input circuit of the detector 15. The output circuit of this detector is coupled to a translating device 16, for ex ample, a telephone receiver.

It is desired to make the detector 15 operative only during the time that signals are not being transmitted by the transmitting circuits, and for that purpose the control wave due to generator 8 is caused to apply a negative potential to the grid of the detector 15 and the grid of the generator 1 alternately. This is accomplished by connecting the output circuit of the power limiting device 9 through switches 17 and the amplifier 18 to the input circuit of the detector 15, the connections being such that the voltages produced by the control source of electromotive force and impressed upon the input circuit of detector 15 are in opposite phase to those impressed upon the input circuit of the generator 1. By this means the generator 1 will be in efficient transmitting condition when the efficiency of the detector 15 is zero and vice versa.

In adjusting this system for operation it will be desirable first to tune for receiving signals with the switches 17 and 11 open and with the transmitting arrangement cut out, then to close these switches and adjust the frequency of the control generator 8 until signals are heard distinctly. It will then be possible to transmit and receive without interference.

The arrangement disclosed may be regarded as a system for two-way repeating to and from a line. The antenna 7 constitutes a signaling conductor or line from which incoming waves pass through the power limiting device 13 and the detector 15 to the receiver 16. When the grid of the detector is made negative by the auxiliary channel 8, the detector is inoperative. hen the detector operating the energy of the high frequency waves passing through it is in part transformed into low frequency energy and sup )liGCl to the receiver 16. On the other hand, waves from tie microphone cir cuit 2 are amplified by the amplifier 3 and combined with waves from the generator 1 to produce modulated high frequency waves at the i'nodulator 4c. The modulated high frequency waves are transferred through the amplifier 5 to the antenna circuit. hen the generator 1 is inoperative, no high frequency waves will be produced and the path 4;, 5 will have a negligible transferring efiiciency :for the speech waves from the circuit 52 because of the relatively high attenuating efi'ect oi the tuned circuit between the tubes 4 and 5. Waves transferred through the input circuit, therefore have their frequency changed during transmission by detection While the outgoing Waves are changed in part by modulation.

Although the invention has been described as applied to a duplex radio signaling sys tem, it is apparent that many or the features are equally Well adapted to use in other radio systems than the kind described and also in Wire systems employing high frequency cur rents varying in accordance with signal it is also apparent that several features or the invention are capable of general application not only to various kinds of signaling sy tems, but also to use in other transmission system What is claimed is:

A tW0-Way signal transmission system comprising separate channels for transmitting in each directioln a space discharge device cooperating with each channel and functioning as an essential element for main taining etiicient transmission therethrough an electrode in each of said devices, and electrical arrangements whereby at a given in stant of time one only of said electrodes is established at such a potential as to render the corresponding device inoperative and thereby render the channel vith which said device is associated. incapable of eiiicient transmission.

2. The method of repeating electrical variations by means of a repeating device which comprises continuously applying the waves to be repeated to said device, and toinatically periodically rendering said de vice inoperative at a frequency Widely ditttt'erent from the frequency oi the Waves to be repeated.

The method of utilizing a thermionic repeater tor the transmission of signals which are transferred by electrical Waves which comprises alternately rendering the repeater operative and inoperative at a frequency which is lOW as compared with the Wave frequency but is so high that each inoperative period is short compared to the shortest signal clement desired to be trans mitted.

4i. The method of operating thermionic repeater which comprises continuously supplying aves to be repeated to the input circuit thereof. and automatically supplying a substantially flat topped Wave to the input circuit.

The method of operating a thermionic repeater which comprises continuously supplying Waves to be repeated to the input circuit thereof, supplying to said repeater at times a substantially constant voltage ot a value adapted to maintain said repeater in onic repeaters a plurality oil" sources of Wave to be rcpealml 5y s id repeaters re spectiveiy. and means T01 rendering said repeaters suhstamially inm erative in cyclic order.

T. A spam disc large repeater. a source oi? I ll es to he repeater 'aherchy and means for .y rendering said repeater operative inoperative for periods large as comared With the time reipiircd for the transmission of :sevei c1 successvc waves to be repeated.

R. A system. comprisi a repeater having an input and an output oi. :uit asource oiapproximal; l tlat topped voltage waves, automatic in ms for a. plying said Waves to said circi a separate soul ,c oil. Waves to be repcatml. and means for deriving repeated waves from said output circuit.

9. A. thermionic repeater including a plu rality of eh circuit connected be tween two of d electrodes. a source of ap proxinnitely at topped voltage Waves, and automatically ope-rut means for applying to said circuit. waves t'ZOliL said source oi? a sufficiently large value to render said repeater inoperative.

ll). space discharge de'vi e including a cathode and an impedance controlling element. and automatic means coiunsrted to said element for varying the potential thereol with respect to the :{mttilltllil of said cathode in accordance with a curve represented by the infinite series and of a lililfiilll-Uill value sullicieut to render said repeater inoperative.

ll. two-way signal transmission system comprising separate channels for transmit-- ting in each direc on. a space discharge device coopertiuu' th each .liillllltl and "functioning s an essential element for maintaining ellicient flilSllllSSlOll therethrough, means "or estahl hi a controlling field of force l or each of said devices. and electrical arrangements whereby at a gia'en iiistaut oil time one only o said liolds of "force is given such a value as Al render the corresponding device inoperative.

1.2. A system including a space discharge epeater. a circuit for supplying Waves to be repeated to said repeater. a source oi? Wavesor lllii'zhtilltlllllt. frequency and [lat topped wave form. and means for applying said. ulti'a-aiu lible Waves to said repeater.

In a duplex transmission system means "for accomplishing transmission in one discharge device, and means acting indepe icntlv of the opr tion of the aforesaid inean; causing devices to be operati and inoperative alternately.

l signaling system comprising a pluruiity of paths lor the transmission of electrical waves, a space discharge device coneuch of said paths, a son. cc of en sourc of electrical Waves for cysaid devices lliOP-firittit. -5cm comprising a siou paths, separate .vaves to each path to transmitted thcrethrough, a space discli-a 'gc repeater coni'icct' each path, a

,cd to r voltage of a value sutiicient to rend repeaters inoperative, and means "plying! said voltage to said repeaters cyclically.

it fr communication system C(Jil'lPI'iSiIlg a plurality of circuits having a fixed state of i-ontinuity and including complete apparatus for the transmission of electrical Waves through each of said circuits, and an inde pendent source of current for alternately rendering said paths opaque to the waves to be transmitted.

i7. A system comprising a plurality of normally symmetrically transmitting Wavetransferring circuits having a fixed state of continuity, and means for cyclically causing said circuits to have. negligible Wave transferring power in the normally transmitting direction thereof.

.18. .lv'ieans for use in transmission systems comprising a source of waves to be repeated, a space discharge repeater for repeating said waves, said repeater including an impedance controlling element, and means for alternately applying to said element and removing therefrom a negative potential of a l'iigher order than the amplitude of the waves to be repeated at a frequency differing from the frequency of said source by a difference greater than an audible frequency.

19. in a signaling system, means for signaling in one direction and means for sig naling in another direction, each of said means including a vacuum tube. and means for acting upon said tubes al ernately to render them substantially inoperative at a frequency rwl lch does not interfere with the transmission of signals.

20. in a signaling system, means including a vacuum tube for signaling in one direction and means including a second vacuum tube for signaling in another direction, a generator of alternating current, and means for supplying current of opposite phases from said generator to said tubes.

2], A duplex signaling system, comprising a generator of high frequency'waves, means for modulating the high frequency waves, a signaling conductor, a receiving circuit containing a detector associated With said conductor, 1 a second generator for controlling the efficiency of said first generator and said detector.

22. 1-; duplex signaling system, comprising a generator of high frequency Wit 6S, means for modlating the high frequency Waves, a signaling conductor, a receiving cir cuit containing a detector associated With said conductor, said generator and said de tector being normally operative, and a. second generator connected to alternately render said first generator and said detector inoperative.

A duplex signaling system, comprising a generator of high frequency Waves, means for modulating the high frequency waves, a signaling conductor, a receiving circuitcontaining a detector associated with said conductor, said generator and said detector being normally operative, and a second generator connected to alternately render said first generator and said detector inoperative at a rate above the limit of audibility.

2a. A duplex signaling system, comprising a generator of high frequency oscillations, means for modulating the high frequency waves, an amplifier, a signaling conductor, a receiving circuit containing a detector as sociated with said conductor and a second generator of frequency above the limit of audibilit-y, so connected as to render said first generator operative and the detector inoperative when its electromotive force is in one direction and to render said first generator inoperative and the detector operative when its electromotive force is in the opposite direction.

25. A duplex signaling system, comprising a generator of high frequency Waves, means for modulating the high frequency Waves, an amplifier, a signaling conductor, a receiving circuit containing a detector associated with said conductor, a power limiting device in said receiving circuit to prevent erzcessive passage of power from the transmitting circuit to the detector, said generator and said detector being normally operative, and a second generator connected to alternately render said first generator and said detector inoperative at a rate above the limit of audibility.

26. A duplex signaling system, comprising a thermionic oscillator for generating high frequency currents, means for modulating the output of said oscillator, an amplifier, a signaling conductor, means for impressing said amplified output upon said conductor, and a receiving circuit including a thermionic detector, second generator of frequency above the limit of audibility so associated with said thermionic oscillalor and detector as to alternately render them inoperal ive.

27. A duplex signalii'ig system, comprising a thermionic oscillator for generating high frequency currents, means for modulating the output of said oscillator, an amplifier, a signaling conductor, means for impressing the amplifier output upon said conductor, a receiving circuit including a thermionic detector, and a second generator of frequency above the limit of audibility and so connected to the input circuits of the first generator and detector as to render said first generator operative and the detector inoperative when its electromotive force is in one direction and to render said first generator inoperative and the detector operative when its electromotive force is in the opposite direction.

28. The method of abtaining an alternating voltage of approximately the characteristic given by the infinite series sin (2N+1)a2,

which consists in generating a uniform voltage of an approximately sinusoidal characteristic. eliminating all voltages above a certain low maximum and amplifying the remainder to the desired value.

529. An alternating voltage generator for obtaining a voltage curve with a flat-topped characteristic comprising a generator of uni form alternating voltage, and a power limiting device for cutting off all voltages above a specified maximum.

30. An alternating voltage generator for obtaining a voltage curve of a flat-topped characteristic comprising a generator of uniform sinusoidal alternating voltage. a power limiting device for cutting off all the voltages above a low maximum, and an amplifier for amplifying the remainder to any de sired value.

31, A voltage generator for obtaining an alternating voltage of approximately the characteristic given by the infinite series,

comprising a generator of alternating voltage of substantially constant frequency and amplitude, a power limiting device upon the input circuit of which said alternatiug voltage is impressed, whereby all voltages above a certain low maximum are eliminated, and an amplifier associated with the output circuit of said power limiting device.

32. Means for producing a voltage wave having a flat topped characteristic comprising a uniform source of sinusoidal voltage of large maximum amplitude as compared with the maximum amplitude of the desired form, a power limiting device whose maximum current capacity corresponds to the maximum au'iplitude of the desired wave, and means for applying said sinusoidal voltage to said device. i

33. A system comprising a line, repeating means associated therewith, and means for automatically reversing the operative repeating direction of said repeating means with respect to said line while repeating without changing its circuital state of continuity with respect to said line.

3%. A modulating system con'iprising a source of high frequency waves to be modulated, a source of low frequency modulatmg waves, means to modulate said high. fre quency waves in accordance with said low frequency waves, an essential element of said system being incapable of functioning when an electromotive force of a certain amplitude and polarity is applied thereto, a source of electromotive force, and means for intermittently applying to said element from said source an electromotive force of sufficient amplitude and such polarity as to prevent the functioning of said element.

The method of cyclically rendering inoperative a plurality of energy transferring channels while maintaining their state of continuity unchanged which consists in cyclically establishing and disestablishing in the space occupied by a portion of each of said channels, a field of force of such a nature as to prevent transmission therethrough.

36. A generator of intermittent oscilla tions comprising a space dischz'irge device having a plurality of electrodes including an electrostatic control electrode, circuit arangements connected thereto appropriate for the generation of oscillations, and means separate from said generator for intermit tently causing on of said electrodes to assume a potential not permitting the generation of oscillations while maintaining fixed the circuit connections of said generator, said generator automatically resuming its generating function when said electrode resumes its normal. potential.

37. A high frequency carrier wave transmission system comprising a space discharge device having metallic circuit connections and a feedback connection for generating and supplying carrier oscillations, a source of space current for said generator, and a continually acting means other than said source for automatically causing said device to alternately become operative and inoperative while maintaining the state of continuity of its metallic circuit connection unvaried.

38. A signaling system including a detector, means for supplying waves to be detected to said detector, a separate local source of waves, and means for automatically supplying Waves from said source to said de tector, said means comprising elements adapted to furnish Waves of such amplitude and polarity as to intermittently prevent the efi'icient detection of the waves to be detected.

39. A two-way transmission system comprising an incoming channel for receiving incoming waves and an out-going channel for transmitting outgoing Waves, a source for supplying to said outgoing channel waves to be transmitted, a separat local source of waves, and means for impressing waves from said source upon each of said channels.

40. A wave transmission system including a space discharge device comprising a source of waves to be transmitted, a second space discharge device constituting a detector for received waves, and continually acting means for rendering said devices operative and inoperative alternately.

41. A radio system comprising a space discharge amplifier having conductive circuit connections and a feed back connection from its output circuit to its input circuit, a source of space current for said device, and a continually acting means other than said source for impressing a periodic electromotive force upon said device to periodically render it alternately active and inactive to feed back and reamplify oscillations from its output circuit to its input circuit while maintaining unvaried the physical state of continuity of its conductive circuit connections.

.2. A receiving system for high frequencywaves comprising a vacuum tube detector having anode. cathode, and electrostatic control electrodes, suitable circuits connecting said electrodes, means including a vacuum tube repeater and a source of waves for varying the electrical condition of a circuit con necting said electrodes at a given frequency much lower than the frequency of the waves to be received, but above the usual audible range and of such intensity as to va y the impedance of said circuit at said given frequency, and an output circuit connected to said detector circuits including a device for producing an audible indication having an audible frequency independent of small changes in said given frequency.

43. The method of receiving high frequency electromagnetic waves by means including a detector which comprises supplying energy derived from the received waves to said detector, also supplying to said detector periodic electrical energy of frequency much lower than the frequency of the waves to be received but above the usual audible range and of such an intensity as to alternately render said detector eflicient and inefficient, and deriving from said detector an audible indication having a frequency independent of small changes in the frequency at which the detector is rendered ineflicient.

In witness whereof, I hereunto subscribe my name this 31st day of May, A. D. 1916.

JOHN MILLS. 

